A Wi-Fi network may be formed by one or more access points (APs) that provide a wireless communication channel or link with a number of client devices or stations (STAs). Each AP, which may correspond to a Basic Service Set (BSS), periodically broadcasts beacon frames to enable any STAs within wireless range of the AP to establish and/or maintain a communication link with the Wi-Fi network. Alternatively, a Wi-Fi network may be formed without an AP, thus corresponding to an Independent Basic Service Set (IBSS).
For most Wi-Fi networks, the IEEE 802.11 standards define a distributed coordination function (DCF) that instructs individual STAs (and APs) to “listen” to the medium to determine when the medium is idle (e.g., using a “carrier sense” technique). The STAs may then contend for access to the wireless medium, and the IEEE 802.11 standards also define medium contention and backoff procedures. Sensing for the wireless medium to become available and then contending for the wireless medium may cause significant delay or inefficient use of the wireless medium. Additionally, sensing requires a device to listen to the wireless medium and thus not be in a low power state.
With carrier sense, some receivers (such as receivers defined by the IEEE 802.11 standards, receivers with the License Assisted Access (LAA) feature as defined by the 4G Long Term Evolution (LTE) protocol described by the 3rd Generation Partnership Project (3GPP), or other receivers) may determine that a channel of the wireless medium is busy or occupied (energy is sensed on the wireless channel to infer that the channel is unavailable). However, use of carrier sensing to determine when a channel is busy or occupied based on the amount of energy on the channel requires inferring when the channel is occupied. For example, the minimum energy levels for detection may be required to be as low as −82 dBm for a 20 MHz channel to prevent a listening device from erroneously inferring that the channel is not occupied when signals on the channel are close to the minimum energy level. As a result, the channel may be inferred to be occupied when the channel is actually available. Additionally, the channel is not determined to be occupied until after the channel actually is occupied. For example, a wireless device may require time to sense whether the wireless channel is occupied to sense energy in transit from the device occupying the wireless channel.